Help on Simulating & Constraining Parts that are not Exact & Defined! 1

[giolf88]

Hi everyone,

Good day!

I need your help regarding an assembly that I want to simulate. My assembly has a composition of a two-stage gear reduction using timing belts and spur gears. I’ve done these components in the Part Design Workbench. I have drawn these in detail and what I want to do is simulate their movement including the meshing.

If anyone among you has seen the “The Holland Project -Digital Mockups of Naval History” Demo CDs, you would notice that at some simulations, the springs and belts are also being simulated realistically. For example, the spring extends and goes back to it original state when a component attached with it exert a force upon it. Also, the belt is animated realistically and was able to maintain the mesh as the gears are rotated.

My question is, how are these accomplished? Is there a specific workbench where these spring and belt done so as they be able to be animated? What specific or special constraints needed to properly mesh the belt and the gear? Or is this all dependent on the joint created in the DMU Kinematics Workbench? And of course, what kind of joint is that? My problem mainly is how to simulate and constraint a part that is not exact and defined? Like cables, belts, springs and the likes. Thank you.

Bunny Boy
Manila, Philippines

 

[jackk]

Bunny Boy...

I happen to currently be working with Gary McCue who is the author of the New Holland digital mockups. I'll pass on your question to him and I'm sure he can tell you what he did. I'd like to know also!

....Jack

 

[gwmccue]

Bunny Boy,

I used a combination of things.

1) I used DMU Kinematics to define all motion
2) I used DELMIA DPM to choreograph everything
3) I used a little smoke an mirrors when absolutely necessary, but tried really hard to avoid it.

For example, in the hatch simulation:

The spring was kinematically modelled as if it were a hydraulic ram. The spring was modelled in two pieces such that when fully extended, it looks like a single expanded spring. As the hatch opens, the two halves slide together such that when the hatch is fully opened, the coils of one spring fit neatly between the coils of the other spring. As a result the spring looks compressed. Watch carefully as the spring opens and closes and you can see the fakery.

The belt drives the bilge pump, which is one of two compenents I did not have the time to animate (the other was the air compressor), so the belt does not actually move. I thought about it though, and planned to define the kinematics for the drive shaft and the pump, then use DELMIA DPM to drive both mechanisms at the same time. This is similar to the way the propeller shafting was done. The clutch was one kinematic mechanism, the intermediate shaft was another, and the propeller shaft was a third. Using DELMIA DPM, I closed the clutch, then activated the intermediate shaft and the propeller shaft simultaneously. Both shafts were made to turn the same number of revolutions in the same time period, which kept the two halves of the dog clutch in the same relative position at all times.

I planned to model an antique crane for the construction sequence, but ran out of time. I this case, I planned to use the kinematic cable function, but visually simulate the motion of reeling in and reeling out the cable using the same trick as I used on the spring. For example, model the cable from the top pulley to the hook as two rods of the same diameter, then simply slide them together when the cable is reeled in, and extend them as the cable is reeled out. If you need to reel in more than half the distance from the top pulley to the hook, break the cable into smaller rods.

Gary McCue

 

[giolf88]

Gary,

Thanks for your reply!

Yes, I do notice the fakery when I checked the simulations again. Therefore, I would assume that there is really no way of Simulating & Constraining Parts realistically that are not Exact & Defined.

I guess that you just have to find workarounds to eventually end up to the desired simulations after all.

Thanks again,
Bunny Boy
DLSU - Manila
Manila, Philippines